Sound absorbing material



il( l' I oooooooooowdoooo OOOOOUOOOOOOOUOOOOOO 0000 OOO 0000000000000Lloloiooloo *\|ooo0000000oooooooo00| 000000000 000000000000000000000000000000 000000000 0000000000 00000000000000000000 00000000000000.00000 lwwmhmv., 00000000000000000000 000000000 0000000000 wAw/a00000000000000000000 000000000 0000000000 oooooooooooooooooooo00000000000000000000 00000000000000000000 000000000 000000000000000000000000000000 0 000000000 0000000000 00000000000000000000000000000 0000000000 00000000000000000000 000000000 000000000000000000000000000000 wwwwwwwwwowwwwwnovwmww 0 ooooooooooooooonvoooOOCOOOOOO 0000000000 j 00000000000000000000 000000000 0000000000 f00000000000000000000 000000000 0000000000 y U 0..,0 J00000000000000000000 ooooooooo 0000000000 0 (2 gdwda00000000000000000000 000000000 0000000000 ,WQ as da! Ga@00000000000000000000 000000000 0000000000 7% un /J 00000000000000000000000000000 0000000000 0 9 9v Jv 00000000000000000000 0000000000000000000/ V9 vff /d/ja 00000000000000000000 000000000 00000000 P KA 6b00000000000000000000 000000000 00000000?. K9/v9 5 j 00000000000000000000000000000 0000000000 n, 9 yDJw/.D 00000000000000000000 0000000000000000000 l @,f fO, 00000000000000000000 000000000 0000000000 v5000000000000000000000 000000000 0000000000 JMrsQ /o .00000000000000000000000000000 0000000000 uff? nvag f 00000000000000000000 \l\ 00000000000000000.00 $18 JJ. .040! 00000000000000000000 7 000000000 0000000000000Y dla i 00000000000000000000 ooooooooo 0000000000 @naald/4. 4,07700000000000000000000 000000000 0000000000 $000.0@ 92 9.900000000000000000000 000000000 oooooooooo ufff p 99V 0000000000000000000 krplull i* ooooooooomoooooooooo vmoovaadaym/df 0000000000000000000 wvvwdr$00 U unido Ouai ,W Afd/o f Patented Apr. 13, 1937UNITED STATES PATENT OFFICE 3 Claims.

This invention relates to improvements in the construction andmanufacture of sound absorbing wall-forming material of the cast ormolded mineral types. Such materials are employed for 5 the control ofacoustical conditions which are present in auditoriums, halls, rooms,theaters, subways or vehicular tunnels where the minimizing of sound andits general correction to establish improved or desirable sound effectsconstil0 tutes an important consideration.

To secure these and other results, porous or cellular wall-formingmaterials have been developed which usually comprise preformed panels orblocks composed in certain instances of heattreated ceramic materialshaving rough uneven exposed surfaces with which the small internal voidsor cells communicate, whereby to receive sound waves or disturbanceswhich impinge thereon to4 absorb such sound and prevent its reflectionas occurs with the use of wall-forming materials having smooth denseexterior surfaces. Such sound absorbing panels of a generally porouscharacter have also been formed by suitably bonding small gradedparticles of a rocklike material in which a cementitious bond is used,Aor by the employment of blast furnace slag crushed into particles ofdesired size and suitably united to produce wall-forming panels. Again,minerals such as cyanite have been rendered cellular 'or porous throughheat treatment in expanding temperatures, and the expanded particlesunited by a clay bonding agent.

There are also other methods of forming these sound absorbing blocks orpanels which produce products varying more or less in their relativeability to absorb or control sound but in general they may be allcharacterized by the rough, porous and uneven texture of their exposedsurfaces. This physical condition makes it very difficult,

and usually impossible, to wash or clean the exposed surfaces of suchmaterials when they are assembled in wall-forming order, and thisconstitutes a serious objection to their use in many cases whereotherwise they would be entirely satisfactory and generally desirable.

It is, therefore, one of the outstanding objects of the presentinvention to provide an improved wall-forming block or panel composed ofa body portion of the desired cellular or porous character formed in anyof the well accepted methods of manufacturing such porous soundingmaterial, as above described or otherwise, and wherein such bodymaterial is provided withan outer facing constituting a relative thincoating of a dense smooth surface material, but wherein is included,

during its process of manufacture, a multiplicity of small closelyrelated openings or perforations which extend to the cells, voids orinterstices of the body material, so that sound waves striking theexposed surface of the facing layer will pass 5 through these openingsor perforations and are thereby absorbed or trapped in the small voidsof the body forming material with practically the same efficiency as ifthe rough texture of the body material were directly exposed to soundcontact. l0 However, due to the presence of the relatively smoothexposed surface of the facing layer, the washing or cleaning thereof maybe accomplished with ease and facility so that the wall-formingmaterial, constructed in accordance with the 15 present invention may bemaintained in a desired state of cleanliness.

To obtain these results, very considerable difficulty was encountered inthe molding of the plastic materials in their formative state.Generally, 20 such sound absorbing materials are rst formed to produce aplastic mass, which is poured into metallic molds in order to producepanels or blocks of desired configuration. It was found to beimpossible, in order to produce the per- 25 forations in the facingmaterial as above described, to provide the bottoms of such metallicmolds with a plurality of upstanding pins or projections for the reasonthat the cementitious or ceramic materials would adhere upon settingwith 30 such pins or projections with such tenacity as to preclude theremoval of the hardened panels or blocks following setting or heattreatment without injury to either the block, panel or mold.

I have discovered, however, that through the employment of a mold formedfrom an elastic material, such as rubber, or wherein the pins orprojections of the mold used in forming the facing openings are composedof such elastic ma- 40 terial, the hardened or molded product maywithout any difficulty at all be readily removed from the mold in afinished, perfected and desired state, this operation being such as toform the openings or perforations in the facing materials 45 in anentirely satisfactory manner and at the same time avoids injury to themold upon the withdrawal of a formed block or panel.

For a further understanding of the invention, reference is to be had tothe following descrip- 50 tion and the accompanying drawing, wherein:

Fig. 1 is a plan view of a panel of sound absorbing material formed inaccordance with the present invention;

Fig. 2 is a vertical sectional view taken through 55 10 Fig. 7 is a.transverse sectional view taken therethrough on the line VII- VII ofFig. 6.

Referring more particularly to the drawing, the numeral I designates ablock or panel of sound absorbing material formed to comprise a body 15portion 2 and a facing layer 3, which may be applied to one or moresurfaces of the body material. The body material-is of a generallyporous character and may be produced in accordance with the disclosurescontained in a prior appli- 20 cation, Serial No. 630,086 filed August23, 1932 led by A. H. Sexton and F. R. Kanengeiser. However, I do notlimit myself to any particular method of forming or producing the bodymaterial, since it is within the scope of the invention to utilize anyof the above described methods for producing a porous or cellular bodythrough the employment of minerals which may be reduced to a moldablestate and subsequently set or hardened by curing or heat treatment.

so One method of forming the body 2 may consist as set forth in theaforesaid prior application, in the employment of crushed substantiallyuniformly graded limestone particles which are first water soaked tosubstantially the limit of their water absorbing capabilities, andwherein dry cement alone is added to these particles, following .theremoval of excess moisture, to provide a bonding medium whereby theseparticles of mineral matter may be united through molding in a o desiredhomogeneous manner, but at the same time producing voids or interstitialspaces 4 between the mineral particles which are known to `be effectivein their ability to absorb and control sound.

In producing my improved product, I employ a mold 5 of suitable shapeand dimensions which includes a'bottom 6, upstanding vertical side walls1 and an open top. 'I'he bottom of the mold is provided with a pluralityof integral, relatively spaced upstanding projections or pins 8 whichare of a length preferably exceeding the thickness of the facing layer 3of the improved sound absorbing material. Preferably, the entire moldin- 55 cluding the projections or pins 8 is formed from live rubber,possessing the ability to stretch or flex quite readily.

In the use of the mold, the materials constituting the facing layer whenin a substantially fluid state, possessing substantially the consistencyof a thick cream, are poured onto and over the bottom of the mold aroundthe pins or projections 8, the depth of these forming materials beingpreferably less than that of the height of the projec- 05 tions 8 sothat the upper ends of the latter will be visible after the facing layerhas been poured. The materials comprising the facing layer may of coursevary greatly, and I have used successfully in one form of my invention acementitious mixture composed of approximately equal parts of a fineOttawa sand and Portland cement, to which I add a sulcient amount ofwater so that the resulting mixture will possess free flowing andreadily moldable properties. If desired, suit- 75 able mineral oxidecoloring matter'may be added to this facing layerl to'prduce desiredcl'o'rueffects, after the disclosures set forth in the prior applicationof A. H. Sexton, Serial No. 633,158 filed September 14, 1932.

Following the placing of this mixture of facing materials in the mold 5,the body forming materials may then be added to the mold toapproximately the height of the side walls 1. These body materialsmaycomprise a plastic mixture composed of crushed minerals ofsubstantially uniformly graded particles of irregular shapes possessingthe ability of absorbing water to an extent varying from 6% to 15% byweight thereof. This material ordinarily is composed of non-metallicminerals having sufficient hardness and permanency so that they will notdisintegrate by elemental exposure and are carefully graded as to sizewithin comparatively narrow limits. Thus in one form of my invention,these mineral particles may be graded between screens composed of from 6to 12 strands to the inch, or between screens of 10 to 20 mesh, or incertain instances 20 to 30 mesh, each grading to be handled separately.

Following the grading of these relatively small, uniformly sized andcrushed or shattered mineral particles, the latter are then wetted byimmersion or sprinkling until they have been saturated with water.Excess water may then be drained off after the mineral particles haveabsorbed substantially 6% to 15% by weight of water. Dry cement,preferably Portland cement, is then added to the water-containingmineral particles and the material agitated to obtain a thorough mixingof the cement with the wetted mineral particles. After this thoroughmixing, which may be done in any character of apparatus, the mixture isplaced on a screen having a mesh size less than that of the particles ofthe aggregates. All excess material, such as unwetted dry cement, isscreened out of the mass, whereby to leave only such cement adhering tothe surfaces of the mineral particles which has been wetted by themoisture present therein.

This plastic material is then placed in the mold 5 on top of the facingmaterials and molded sufilciently to cause the cement coatings, whichsurround each of the mineral particles, to coalesce or bond with similarcoatings on adjacent aggregate particles. The resultant material, afterit has been allowed to dry and harden, comprises a porous product with avariety of interstices of different sizes communicating with one anotherand formed in said body between the individual cement coated particles.It is important that the material used as an aggregate should be theproduct of a crushing operation, so that there Will be formedirregularly shaped pieces and all approximately of the same size,whereby when this mass is cemented together, the interstitial pores orpassages of varying area will be produced. My invention thus provides anacoustical material of high sound absorptive value and at the same timea material which is highly fire resistant. When the molded product isremoved from the mold, following the usual curing period, the facingmaterial is integrally united with the body material so that there canbe no separation therebetween. The removal of the molded product fromthe mold takes place easily and without the aid of machinery. This isdue to the fact that the mold proper is flexible and, as stated, isformed from rubber. If there is any tendency on the part of theprojections or pins 8 to adhere to the walls of the perforations 9formed in the facing material, this tendency is immediately relieved bythe stretching of the pins 'or projections, which results in decreasingtheir diameter so that they readily pass out of the perforations 9.Similarly, the side walls 'l of the molds may be readily disengaged fromthe marginal edges of the mold block or panel I. Furthermore, there islittle or no tendency of the material to cling l0 to the `rubbersurfaces, and there takes place a sharp separation which leaves the moldin a cleanly condition, particularly at its corners, so that it isunnecessary to subject these molds, as is the case with metal molds, tothorough cleans- 15 ing before they can be re-used.

There are numerous other advantages attending the use of the rubbermold, tray or palette in the manufacture of moldable products of thecharacter set forth. By the use of rubber,'I can 20 obtain veryintricate surface designs, also duplicate all sorts of fabric designs,wood grain or other patterns of a like nature. The use of rubber in themold formation also permits of convenience in the casting of theseintricate designsand the 25 stripping of the molded article from themold.

Furthermore, it allows one to cast models in relief where under-cuttingis necessary and gives a high degree of density and surface ilnish.These advantages are true whether the material 0 is employed for usesother than as an acoustical wall material.

It will be noted that the peg-like projections 8 are extended upwardlyfrom the bottom of the mold a sufficient distance to penetrate into the35 mass of the acoustical body material. The facing material, it wouldseem, apparently increases the total sound absorbing capacity of thematerial rather than to decrease it. 'I'his undoubtedly is due to thefact that once the sound wave has 40 penetrated through the perforations9 into the inter-communicating cells or pores of the body material, andthe solid facing holds a greater percentage of the sound wave within themass of the body material until it finally dies. By this 45.method andconstruction, an improved sound absorbing material is produced both fromthe standpoint of its capacity to absorb sound and in addition, theimprovement in appearance and cleanliness afforded the product by theouter facing. 50 ,as stated, this racing may be made up in a variety ofpatterns or to produce dierent color eifects, which fact materiallycontributes to its usefulness as a wall material.

In the form of our invention disclosed in Figs. 55 6 and "I, the blockor panel is indicated by the numera1 I0 and is 'formed by firstproducing a primary fluid-like mixture composed principally of sand,cement and water so that it may readily flow over the bottom of apan-shaped mold, simi- 60 lar to that disclosed in Fig. 4 with theexception that the upstanding pegs or projections are omitted. Thisprimary mixture is distributed over the bottom of the mold in the formof a relatively lshallow layer of approximately the same 6* depth orthickness as the facing layer 3 in the previously described form ofblock. We then substantially fill the balance of the mold with theporous body mixture which corresponds to that employed in the making ofthe body 2 with the exception that it is in a somewhat drier state sothat this body material which is indicated by the numeral II, while theprimary or facing layer is indicated by the numeral I2, will absorbmoisture from the facing layer at such a rate as to produce amultiplicity of relatively small irregular openings or passages in theprimary layer, which extend completely through the latter in order toestablish sound communication between the exterior of the block and theinternal voids of the body layer. 'Ihis form of block or panel, like thepanel I, also presents a smooth finished exterior surface which may bereadily cleansed by being washed or otherwise renovated. So far as weare aware, a sound absorbing materialhaving this property of beingreadily lcleansed or renovated is generically new and the claims herein-Iafter made are therefore to be construed ac-l cordingly.

What is claimed is:

1. A molded wall unit for acoustical regulation comprising a porous baseformed from a plastic molded composition of small uniformly sizedcrushed mineral particles united by a cementiousbinder and having formedtherein a multitude of interstitial passages or voids between themineral particles, and a facing layer having a smooth exterior surfaceintegrally bonded onits inner side with said base, said facing layerbeing composed of sand and cement and having molded therein a largenumber of relatively spaced transversely extending openings for thetransmission of extraneous sound to the sound absorbing voids andinterstices ofsaid base.

2. A molded wall unit for acoustical regulation of fixed determinabledimensions, comprising a base composed of uniformly sized mineralparticles united by a cementitious' binder to form a homogeneousmaterial having disposed therein a multitude of interstitial passages orvoids betweensaid particles, and a facing layer integrally bonded on itsinner side with said base, said facing layer being composed primarily ofsand and cement and having molded therein a large number ofk relativelyspaced transverselyfextending openings for the passage of sound energythrough said facing layer.

3. A building unit of predetermined dimensions comprising a basecomposed of crushed substantially uniformly graded limestone particlesand a cementitious binder permanently joining said particles to producea homogeneous composi-l tion having throughout its structure a multitude4

